function LimitDrag(id) {
	Drag.call(this, id)
}
// console.log(Drag.prototype)
for (let key in Drag.prototype) {
	LimitDrag.prototype[key] = Drag.prototype[key]
}
LimitDrag.prototype.fnMove = function(ev) {
	var oEvent = ev || event;
	var l = oEvent.clientX - this.disX;
	var t = oEvent.clientY - this.disY;
	if (l < 0) {
		l = 0
	} else if (l > document.documentElement.clientWidth - this.oDiv.offsetWidth) {
		l = document.documentElement.clientWidth - this.oDiv.offsetWidth
	}
	if (t < 0) {
		t = 0
	} else if (t > document.documentElement.clientHeight - this.oDiv.offsetHeight) {
		t = document.documentElement.clientHeight - this.oDiv.offsetHeight
	}
	this.oDiv.style.left = l + 'px'
	this.oDiv.style.top = t + 'px'
}
